- 3 months ago
The Wild West where prairie dogs live in huge colonies known as `towns'. Like meerkats, they are comical to watch, but there is a lot more to prairie dogs than just being cute - they can talk. For 30 years Professor Con Slobodchikoff has been recording their calls in response to predators, and he believes he has discovered a language second only to humans in its complexity.
探索了美国西部草原犬鼠复杂的社会生活，重点关注它们庞大的地下巢穴（“城镇”）以及它们出人意料地复杂且富有描述性的警报语言
探索了美国西部草原犬鼠复杂的社会生活，重点关注它们庞大的地下巢穴（“城镇”）以及它们出人意料地复杂且富有描述性的警报语言
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AnimalsTranscript
00:17The North American Prairies, home to the bison.
00:23But this film isn't about the bison.
00:26It's about a tiny creature that lives beneath the bison's feet.
00:33The Prairie Dog.
00:36You might easily overlook the Prairie Dog until it opens its mouth.
00:44It's a little animal with a big voice.
00:49A team of scientists believe this noise is in fact a very complex language.
00:56Which is remarkable for an animal many see as lowly vermin.
01:01So, what are they saying?
01:04To find out, scientists have devised a set of cunning experiments.
01:13But could these barks, squeaks and chirps really be a language?
01:32To our human ears, this just sounds like a lot of unnecessary noise.
01:36But to other Prairie Dogs, it's all part of a jolly good conversation.
01:42That is, if you believe this man, Prairie Dog expert, Professor Kon Slobochikov.
01:48Prairie Dogs have the most complex natural language that's been decoded so far.
01:54They have words for different predators.
01:58They have descriptive words for describing the individual features of predators.
02:05So it's a pretty complex language that has a lot of elements.
02:10A relative of the squirrel with a language second only to humans in its complexity?
02:16That's a bold claim.
02:19But Kon has a problem.
02:21He's fighting an inbuilt prejudice against these little rodents.
02:25Convincing the wider world that Prairie Dogs are great linguists is proving a tough challenge.
02:32He believes if we just get to know them a little better, understand their world, then we might just see
02:38his point of view.
02:41Life as a Prairie Dog is complicated.
02:45It's not just a simple matter of eating grass and minding your own business.
02:51You have to share your space with lots of other Prairie Dogs.
02:58Every Prairie Dog is part of a big community called a town.
03:04The largest Prairie Dog towns stretch over tens of miles.
03:08Their excavated homes pockmarking the prairie landscape.
03:15Living together requires impeccable social skills.
03:20Kissing is all the rage in Prairie Dog Town.
03:22A little taste of saliva is like a calling card that helps identify a visitor.
03:30Prairie Dogs, though, are nervous creatures.
03:32Always on the lookout for signs of trouble across town.
03:38But what is there to worry about?
03:43Prairie Dogs aren't the only animals living in the town.
03:50Squatters have moved in to some of their vacant burrows.
04:01All these strangers make Prairie Dogs a little nervous.
04:05And so they should be.
04:08Prairie Dogs are under attack from all quarters.
04:13There are times when they must feel besieged by animals that want to eat them.
04:18Even when they retreat to their underground burrows,
04:21the Prairie Dogs can't really relax.
04:35With no safety anywhere, above or below ground,
04:39Prairie Dogs have come up with a clever strategy for dealing with these threats.
04:45Prairie Dogs, they shout very loudly.
04:51Technically speaking, it's an alarm call.
04:58You might still be wondering why Con would choose such a humble subject to study animal language.
05:03After all, there are more likely animal linguists, whales, or monkeys.
05:10But there was something about those Prairie Dog alarm calls that piqued his interest.
05:16With so many predators living in Prairie Dog Town,
05:20Con wondered, do the Prairie Dogs have just one call,
05:23or do they have different calls for the different predators?
05:27There's only one way to find out.
05:30Con must test their calls.
05:35He's on his way to a remote ranch in the north of New Mexico.
05:39It's a haven for Prairie Dogs.
05:42Two species live here, Gunnison's and Blacktail's.
05:47Joining him are two of his students,
05:49Patricia Dennis, who will help record the calls,
05:51and Bill Briggs, who's devised a series of experiments to test the Prairie Dogs.
06:00Together, this team hopes to show once and for all that we have underestimated the little Prairie Dog.
06:18First of all, Con looks for signs of predators in his research area.
06:23Here's a badger excavation.
06:25This is very fresh.
06:26It probably happened in the last day or two.
06:29This is the way that badgers typically hunt.
06:32They'll excavate a Prairie Dog burrow, and then go inside, and while the Prairie Dogs are sleeping,
06:37they will eat the Prairie Dogs, and then they'll also sleep inside the burrow.
06:42And they typically excavate a number of burrows all around us in a particular area,
06:47and then they move on to another place once they've eaten all the Prairie Dogs that live in a particular
06:53burrow system.
06:57The presence of predators is welcome news for Con.
07:01The Prairie Dog should be on a state of alert, and that'll mean good alarm calls.
07:07But waiting for predators to appear would be far too time-consuming.
07:13These imaginative scientists have a solution.
07:16They bring their own.
07:29Time to set up the first experiment.
07:34Bill must keep the dummy predator under wraps while he finds a suitable spot.
07:41Some Prairie Dogs are already a little spooked.
08:00Con uses his car as a screen to hide behind.
08:04It's important that no one is visible.
08:09Those are certainly being vocal.
08:14What's really wonderful about this is that other individuals are chiming in just in response to the vocalization,
08:22so they don't even have to see the stimulus in order to know that this is a coyote, and they
08:27start yelling.
08:30Every call recorded must subsequently be analyzed by Con.
08:35We can hear the difference in the calls between the different predators, but that's not really enough for us.
08:41What we really need is some sort of analytical tools for measuring what the frequency and time elements in the
08:48call are.
08:49And so this software here allows us to do this.
08:54This is an alarm call elicited for a coyote, and we can hear that it has a series of rhythmic
09:03chirps.
09:04Let me stop it at this point.
09:07We think that each prairie dog has its own individual unique tonal qualities,
09:14just like humans have different voices and different voice prints.
09:17But even though each individual prairie dog might differ,
09:21all the prairie dogs have a common call for a coyote, even within those individual voice print differences.
09:28So we think that when a prairie dog is calling for a coyote,
09:31they probably know who the individual prairie dog is that's calling,
09:35just the same way that we can, on the telephone, hear somebody's voice
09:39and immediately recognize it as a person that we know.
09:43The second experiment isn't quite ready.
09:47Bill and Patricia need to apply the finishing touches.
09:51We got this badger off of eBay, and he was a completely prepared skin,
09:56except he didn't have any stuffing inside of him.
09:58So actually what we're doing now is we're placing stuffing in him to give him shape.
10:04Like most Americans, when I first knew about prairie dogs, I didn't know much about them.
10:08I thought they were just rodents, you know, bottom line.
10:13Now I've learned that after, you know, thousands of years of evolution,
10:17they're an incredibly complex social animal.
10:20And every day I work with them, I learn more and more and more
10:24and realize how little I actually know about them,
10:26especially in their communication and social interactions.
10:32And there you go, all ready to hunt prairie dog.
10:39Everything is ready for experiment number two, the stuffed badger.
10:53Con and his team are very excited by this one.
10:56This is the first time they've ever tested a badger.
11:00Will the prairie dogs have a specific alarm call for it?
11:15Well, the prairie dogs are certainly calling.
11:18But are these calls different from the earlier ones to the coyote?
11:23Con hopes so.
11:30The ebay badger has done all it can.
11:33Now the researchers must take a look at all the recordings from today's experiments.
11:38The badger call is an entirely new call for us.
11:42We've never recorded a call for a badger.
11:44So it's really exciting to look at the structure of this call and see what it looks like.
11:49And it looks very different from any of the other calls that we've recorded.
11:53Let me play these calls for you.
12:06To Con's expert ears and eyes, there is a difference, both in their calls and in the shape of their
12:12sound graphs.
12:19The shape of each sound curve varies subtly, but is consistent for each predator.
12:29But to convince any would-be doubters, Con has another experiment planned.
12:38Over his 30 years of research, he's noticed that prairie dogs react in different ways to different predators.
12:45If the alarm calls for coyote and badger do indeed differ, then playing back the two calls to a group
12:51of prairie dogs should produce distinct responses.
12:56Bill's big speakers get fired up.
13:02First, the alarm call for coyote.
13:06The prairie dogs react instantly.
13:17Having spooked one part of the colony with the loudest alarm call they've ever heard,
13:22the team moves on to an undisturbed spot to try out their second alarm call, the badger.
13:38The reaction is very different.
13:49We had a terrific response, and for the coyote call, they did just what they're supposed to do for a
13:54coyote.
13:55They ran to the burrows and stood at the lip of the burrows and watched.
13:59And for the badger call, they ran to the lip of the burrows and crouched down, just like they're supposed
14:04to for a badger.
14:05So it was a terrific result.
14:08Adopting different tactics for different predators makes perfect sense.
14:13A coyote will hunt by surprise.
14:16So perhaps it's safest to sit up and keep an eye on it at all times.
14:21Badgers are the bulldozers of the predator world.
14:24They will dig into a prairie dog hole.
14:27Crouching down might be a way of hiding yourself so the badger doesn't choose your burrow.
14:42It's been a good day for the team.
14:44Every new alarm call is a new addition to their dictionary of prairie dog words.
14:52But there's still a long way to go in their quest to prove that prairie dogs have a complex language.
15:16It's early morning and the prairie dogs are already up.
15:20Breakfast isn't particularly exciting.
15:23It's the same as lunch and dinner.
15:24Grass.
15:27Occasionally, an adventurous prairie dog will opt for something a bit more daring.
15:34The size of a prairie dog territory will depend on the quality of the local grass.
15:39But even where prairie dog numbers are high, there's usually enough for other animals.
15:45The prairie dogs are about to have their breakfast rudely interrupted.
15:50Conn and his team are back and they're keen to try a new test.
15:53One that's a lot stranger than their earlier experiments.
16:00Conn has a hunch that prairie dogs have unique calls for colors.
16:11It sounds a bit mad, but he's putting it to the test.
16:17Patricia is doing a colored shirt experiment.
16:20The idea here is to test the ability of the prairie dogs to discriminate between different colors
16:27and how they incorporate that information into their alarm calls.
16:36No joy.
16:37The prairie dogs aren't calling.
16:42I think one problem is that Patricia is not threatening enough.
16:47She tends to walk slowly and is kind of relaxed about it.
16:51I wonder if we could get Bill to wear a shirt.
16:56Time to substitute Bill for Patricia.
17:01Bill's manly walk provokes a response.
17:06But behind this quirky experiment is a bigger question.
17:10Could the prairie dog calls actually contain more information than just the identity of the threat?
17:16Could they be describing precisely what they see?
17:21Conn believes the answer is yes.
17:25Throughout his 30-year study, he's found that changing the speed, direction and even the color of a threat
17:31results in a change in the prairie dog's alarm call.
17:38We think that each one of these chirps contains a noun-like word
17:43and it also contains adjective-like words
17:46which describe the color, the size,
17:49and all of that is put together into one of these single chirps
17:52pretty much the same way that we would put together a sentence.
17:56So we might say a tall, skinny coyote with yellow fur
18:03and the prairie dogs managed to put all of this into a single chirp.
18:10In other words, prairie dogs can cram into one short call
18:14the same amount of information found in a human sentence.
18:18Makes our language seem a bit long-winded.
18:20Why use ten words when you could just say it all in one chirp?
18:26How do they do it?
18:28Conn suspects the answer lies in the fine detail of their calls.
18:34Each alarm call or each chirp is a series of stacked harmonics
18:40that you can see one on top of the other.
18:43But instead of being actual multiples of the base frequency,
18:47they're actually modulated by the vocal apparatus of the prairie dog
18:51and that's what contains the information about
18:54that this is a coyote as well as the general color and size and shape of the coyote.
18:58That the prairie dog is much more complex than we thought.
19:03This is no surprise to the man who has doggedly championed prairie dogs his entire career.
19:11Everything about prairie dogs points to them being complex animals,
19:16even their homes.
19:18This is a prairie dog hole.
19:21It is part of an elaborate burrow system that is underground.
19:26The hole goes down maybe about between one and three meters
19:31and then the entire burrow system stretches out for anywhere between three and five meters
19:37with a fairly elaborate structure.
19:41There's a bathroom chamber where they pee and poop
19:45and there's a nest chamber where they sleep.
19:49There's also side chambers where one prairie dog coming down
19:54meets another prairie dog coming up
19:56and one of them backs into a side chamber
19:59so that the other one can go past
20:01just like two cars on a narrow, winding mountain road.
20:07The prairie dog burrow system is remarkably sophisticated in its engineering.
20:17And it's deep underground where the pups are born in spring.
20:25Blind and without fur, they huddle together for warmth and security.
20:33This underground world of prairie dogs is rarely observed.
20:59It will be five weeks before the pups are ready to leave their nursery chamber.
21:04When that moment arrives, Conn will be there.
21:07The pup calls will be crucial to his work.
21:18Above ground, the mounds are designed to funnel rain away from the holes
21:22and so keep their burrows dry.
21:26The hard work by these mining rodents
21:28has created a vast infrastructure
21:30that makes the prairies attractive for other animals.
21:35Many different species of all shapes and sizes
21:38have come to rely on prairie dogs for their lodging.
21:47Even the bison,
21:48the largest animal on the prairies,
21:50benefits from having prairie dogs as neighbours.
21:54And it's not just because their burrows are a convenient place
21:58to have a good scratch.
22:04When people think of the American prairie,
22:07they usually think of the bison.
22:10Historically, there were about 30 to 60 million bison prior to 1800.
22:14But they tend not to think of prairie dogs,
22:17where historically there were 5 billion prairie dogs,
22:21coexisting very nicely with the bison.
22:23And the prairie dogs were the ecological engine
22:26that tended to drive the prairie ecosystem.
22:30They would clip vegetation,
22:32and as the vegetation would re-sprout,
22:34this was very nutritious for the bison
22:37and other large herbivores.
22:38And the burrows of the prairie dogs
22:41provided refuges for hundreds of animal species.
22:46So bison and prairie dogs
22:49and other species in the prairie ecosystem
22:52coexisted very nicely for thousands of years.
22:58So for the bison,
23:00the cropped grass that regrows around a prairie dog burrow
23:03is lush.
23:07The prairie dog should be the hero of the prairies.
23:11After all, without them,
23:12the prairies as we know them would vanish.
23:15But humans have somehow turned them into villains.
23:20And we like to kill our villains.
23:26For the last couple of hundred years,
23:29human settlers have waged a war against the prairie dog.
23:35As the Wild West was tamed
23:37and prairie turned over to ranching,
23:39a finger of blame was pointed at the prairie dog.
23:43It was labelled a thief,
23:45falsely accused of stealing the best grass.
23:48A bounty was placed on its head.
23:51Shooting was one option.
24:08Pumping sulfur smoke into their burrows
24:10was a more hazardous alternative.
24:17But it was a government programme of mass poisoning
24:20with strychnine-laced feed
24:22that had the biggest impact on prairie dogs.
24:28The land was being tamed for cattle
24:30and there was no room for vermin.
24:37In little more than a hundred years,
24:39their numbers dropped by a staggering 98%.
24:45And by killing prairie dogs,
24:47humans were slowly killing the whole prairie.
24:54Only recently have we come to recognise
24:57that without prairie dogs,
24:58the prairies would be lost forever.
25:02They're important to all life on the prairies,
25:07including lots of animals that want to eat them.
25:13Conn believes this relationship with other animals
25:16is the main reason why prairie dogs
25:18have developed a complex language.
25:21So what happens to the language
25:23if you take away all the predators?
25:28There's only one place
25:29where he can find the answer to that.
25:36At a zoo.
25:43These prairie dogs
25:44have been in captivity all their lives.
25:47They've never seen predators.
25:58So what will happen
25:59when Bill and Patricia
26:01introduce their dummy predators?
26:07Will these captive prairie dogs
26:09have a call for threats
26:11they've never seen before?
26:20The coyote makes its entrance.
26:31Well, they're certainly calling.
26:33But are they saying coyote?
26:35Right now we've got about eight mics in here
26:38to make sure that we've got
26:40no problems with echoes
26:41or any other apparitions.
26:42And we're recording
26:44the prairie dog's call to a coyote.
26:46And I'm watching it here
26:47on the computer screen
26:49to look at the spectrograph
26:50to see how it's formed.
26:53And to tell you the truth,
26:54it's completely different
26:55than what we're used to.
26:56You still have individual chirps,
26:58but they have no definition to them.
27:00They're completely different.
27:01And it's really surprising to see.
27:05They're making a noise,
27:07but it doesn't sound
27:08like a prairie dog word.
27:12Now, it's the badger's turn.
27:19Is he doing anything
27:20or just looking at it?
27:22So there's actually
27:23two prairie dogs right now
27:24calling.
27:25There's one calling
27:26behind the badger
27:26and another prairie dog
27:27by the middle grate.
27:33I've got a badger
27:35sitting out there
27:36and we've got two prairie dogs
27:37calling for it.
27:38And the spectrograph is just,
27:40it's amazing.
27:41It's nothing like
27:42we've seen before.
27:43We've got the chevrons,
27:44but there's no structure to them.
27:48Their calls are like a scream.
27:50It's an alarm,
27:51but without any meaning.
27:52It suggests they only develop
27:54their words
27:55after repeated exposure
27:57to predators.
28:00If so,
28:02that's learning
28:03and that's a key characteristic
28:05of a proper language.
28:09Bill and Patricia's results
28:11from the zoo
28:12show that animals
28:14who have been
28:15in a zoo setting
28:17for at least nine years
28:18who have not heard
28:19any predator calls
28:20probably lose
28:22their predator calls
28:24or lose the ability
28:25to make those calls.
28:26The zoo animals
28:27have very non-specific,
28:30noise-like calls.
28:31And so I think
28:32that this shows
28:33that learning is important
28:35in this animal language.
28:38This is a major discovery.
28:40Learning is a crucial element
28:42of every language.
28:43But can Con build
28:44on the zoo results
28:45and demonstrate learning
28:47is taking place
28:48out on the prairies?
28:50If prairie dogs
28:52are learning their calls,
28:53then it must be happening
28:54once the pups
28:55come above ground.
28:57This, after all,
28:59is the first time
28:59they'll see other animals.
29:03Testing their ability
29:04to learn
29:05will be the most important
29:07experiment of all
29:08to prove that prairie dogs
29:09have a complex language.
29:12Con's reputation
29:13and the reputation
29:14of all prairie dogs
29:15now depends on the pups.
29:21In early June,
29:23the pups are just taking
29:24their very first steps
29:25above ground.
29:30Con and Patricia split up
29:32to try and find
29:32a good gathering of pups.
29:38It's not long
29:39before their efforts pay off.
29:59But what are they doing?
30:09This morning,
30:10we saw two juveniles
30:12frantically just
30:13shoving grass
30:14in their mouth.
30:16All they think about
30:17is bedding
30:17and shoving it
30:18in their mouth.
30:18And they come all the way
30:19to the burrow
30:20and they just kind of
30:21look out
30:22and they go back in
30:23and they actually
30:24take all these grasses
30:25and stick them
30:26in their burrow.
30:37Perhaps the pups
30:39learn from their parents
30:40how to collect bedding
30:41for their burrows.
30:43Keeping a tidy room
30:44is all part
30:45of growing up.
30:49But there's time
30:50between chores
30:51to relax
30:52and have fun.
30:53and have fun.
31:22all this play
31:23isn't helping
31:24Con and his team
31:25with their research.
31:26They need to focus
31:27the pups' minds
31:28on something
31:29more serious.
31:34Bill is setting up
31:35an experiment
31:36with a new
31:37fake predator.
31:43But what on earth
31:44is it?
31:56This is a silhouette
31:58of an airborne predator
31:59like a hawk.
32:02And we'll shoot this
32:03down this line
32:04to try and simulate
32:05a hawk attacking
32:07a prairie dog
32:07in the colony.
32:08And it should be
32:09pretty exciting to see.
32:10here are
32:12That's.
32:28Here are
32:29things
32:30and
32:30of
32:33thegregious
32:34are out
32:35and
32:35the
32:35Sherlock
32:35and
32:35you
32:36sort
32:39of
32:40that
32:48Not a squeak from the young pups.
32:50First time wasn't as successful as we hoped for,
32:53so we're going to try this again.
32:57Now, come on, class. Pay attention.
33:15Well, this is pretty disappointing.
33:17We've done this experiment before in the past,
33:19and the animals at other sites
33:21have given a characteristic hawk call,
33:23and then they run to their burrows.
33:25But here, they just simply run to their burrows,
33:27and they don't give a call.
33:29Maybe they don't see any aerial predators,
33:32and so have no reason to give a hawk call.
33:34But nevertheless, it's really disappointing.
33:39OK, it's a failure,
33:40but let's not get in a negative state of mind.
33:44Perhaps prairie dog pups are a lot cannier
33:46than we give them credit for.
33:48Maybe Bill's fake hawk
33:50wasn't quite realistic enough for them.
33:54In other areas, prairie dogs often come face-to-face
33:58with the real thing.
34:02Feruginous hawks love to catch prairie dogs,
34:05especially when they have hungry youngsters to feed.
34:26This is more like it.
34:29A swooping hawk is enough to create a state of panic
34:33like in prairie dog town.
34:42Many prairie dogs will go underground.
34:51If the aerial approach isn't successful,
34:54then the hawk has another strategy.
34:57Just sit and wait.
35:05And wait.
35:10The one thing you don't want to do
35:12is go above ground.
35:14Not when there's a big hawk outside.
35:17But pups can be a little impatient.
35:21A hawk can hold prairie dogs hostage like this
35:25for many hours.
35:27Both the prairie dogs and the hawk want to feed.
35:31It becomes a battle of wills.
35:52Eventually, the pups claim victory.
36:13Back at his study colony,
36:15Con is worried that there aren't as many predators
36:17as he thought.
36:18And that's making it difficult to record pup calls.
36:25He needs to get the colony on a higher state of alert.
36:28So he has a plan to stir things up a bit.
36:41Hi, Brent.
36:42Hey, Con.
36:43How you doing?
36:44Hey, good to see you.
36:45Good to see you.
36:45So these are your dogs?
36:47Yep, these are my two dogs.
36:48This one's Rita.
36:49Hi, Rita.
36:50And then we have Izzy over here.
36:52Hi, Izzy.
36:53They're half sisters.
36:54Wonderful dog.
36:54Oh, you want to be petted.
36:56And when they're not chewing on each other,
36:58they like to go after varmints like prairie dogs.
37:02So can we let the dogs out?
37:03You bet.
37:04Super.
37:06Come here, Izzy.
37:09Come here, Rita.
37:10Come here, Rita.
37:13Okay, go get them.
37:14Look at them go.
37:16Yeah.
37:22The purpose of this is to get the prairie dogs more used
37:26to having predators around.
37:28This colony probably has not had very much predation
37:31and they aren't calling as much as I would like.
37:35And so having the dogs running around gets them more alert
37:38and gets them to call more for other stimuli
37:42like some of the other experiments that we're going to do.
37:47This isn't the first time Conn has introduced prairie dog to real dog.
37:53What we found in the past is that they do recognize individual dogs.
37:57They can describe the shape of the dogs, the size of the dogs
38:01and the coat color of the dogs.
38:05But have the dogs had the desired effect?
38:07Have they stirred up this colony?
38:10Only one way to find out.
38:27The pups seem to be on high alert.
38:30But will they call?
38:41Everything is in place.
38:44Now it's all down to the pups.
38:48The tension is becoming unbearable.
39:10The plastic coyote has worked its magic again.
39:14But are the pups actually saying coyote?
39:20If, as Conn suspects, the pups learn the alarm calls,
39:24then at this early stage of their lives,
39:26he wouldn't expect them to know the calls for different predators.
39:32Every call recorded will be subjected to stringent scientific analysis.
39:42But at first glance, the findings look positive for Conn.
39:46Now he does have the same number of calls per series, it seems like,
39:50and the loudness and everything else is the same.
39:52And maybe the loudness and the number of calls is something that is innate,
39:57and maybe the structure is something...
39:59Side by side, the adult and pup calls are very different.
40:04We have here a pup and an adult calling for the coyote.
40:09They sound very different, and they also look very different on the computer.
40:20We can see here the adult call has a lot of structure in it,
40:24and it contains a lot of information.
40:26The pup call, on the other hand, doesn't have very much information in it,
40:31and it changes in structure, just like babbling in little kids.
40:36So this pup is gradually acquiring more and more structure.
40:41As in any language, the youngsters must practice getting the words right.
40:46In human babies, we call it babbling,
40:48and it appears that prairie dog babies babble too,
40:52as they struggle to make the right call.
40:54These results are good news for Conn,
40:57but they don't prove they're learning, not yet.
41:00To really show that...
41:08As the summer draws on, Conn keeps an eye on the young prairie dog's progress.
41:14He needs to find the right moment to test them again.
41:19With a change in season just round the corner,
41:22the last thing on the pup's minds is passing a language test.
41:26They need to make the most of what the prairie has to offer.
41:34There is just one major obstacle to Conn and the prairie dogs,
41:39the monsoons.
42:00July and August are the wettest months of the year,
42:04and prairie dogs are often forced to retreat underground.
42:15All that hard work building their elaborate burrow system has paid off.
42:21They can keep nice and dry, while the rest of the prairie gets soaked.
42:26But too many days spent underground is valuable feeding time going to waste.
42:33Might as well have a little nibble of your bed to keep hunger at bay.
42:51During the heaviest of rains,
42:53prairie dogs can end up trapped below ground for days.
43:02Eventually, the sun returns to the prairie,
43:05and the pups are the first above ground.
43:11Patricia is keen to find out how this year's pups are doing.
43:15But her presence is making someone very unhappy.
43:24There's an individual over there calling randomly for us.
43:27In the field, we actually call those nervous Nellies or worried Willies.
43:31They really aren't important in the colony, per se.
43:34Some of the individuals will stand up and actually take notice of this caller,
43:38but they really won't pay attention.
43:41It's kind of like the boy who cried wolf too many times.
43:44After a while, they just stop believing this guy.
43:47So he's really just a nuisance when we're in doing field work,
43:51because we're really not sure what he's calling for.
43:52But he just keeps going on and on and on and on.
43:58Crying wolf isn't good for anyone.
44:00You might not take notice when real danger threatens.
44:04And that could be a big mistake.
44:11A prairie rattlesnake is taking an afternoon slither through Prairie Dogtown.
44:20The pups have been resting during the heat of the day.
44:38This isn't the time to take a nap.
44:41Not when a rattlesnake is on the search for a burrow.
44:45And perhaps even a snack.
44:51A call meaning, wake up, would be really handy in this situation.
45:09It's looking a bit dicey for this little chap.
45:27But let's not forget, prairie dog burrows have more than one way in and one way out.
45:36It's a cool, last-minute getaway.
45:41Leaving the snake hungry.
45:43But at least it's found somewhere to shelter.
45:54In late summer, the rains bring a flush of colour to the prairies.
46:14In late summer, the rains bring a flush of colour to the prairies.
46:41For the prairie dogs, it's been a pretty boring diet until now.
46:45But sunflowers will provide a tasty treat.
46:51Each sunflower seed has twice the number of calories as a blade of grass.
46:56So they're vital to the prairie dog pups as they fatten up for the winter.
47:16It's getting late in the season.
47:19Con, Bill and Patricia must get on with their final experiments before the first fall of snow.
47:36Adult prairie dogs have already gone below ground for winter.
47:40But the pups still need to carry on fattening up.
47:44Time to set up their final exams and see how their vocabulary is shaping up.
47:49Are they still babbling like babies or talking like adults?
47:53Out come the usual suspects.
47:58Finance is a big fluke for desnanny to even talk.
48:06In previous
48:06delivery of shrогда.
48:06Personal spurious adventure falls.
48:10Can you see how it looks like a big event?
48:17To add up our own pou recycel.
48:18Our great show.
48:25Have a nice day,ů.
48:26We've got a really distinct coyote call.
48:29There's another one calling from across the colony.
48:53Okay, Bill, let's do the badger.
49:10They're standing up where they're foraging and looking to see where the badger is going.
49:14And that's different from a coyote.
49:16For the coyote, they run to the lip of their burrow and stand there.
49:20For the badger, they are a little bit more reluctant to run to their burrow
49:25until they see which burrow the badger is going to.
49:29The signs are all good.
49:31They're at least reacting in the right way to the fake predators.
49:45The pups seem to be in fine voice.
49:49But have they learnt the proper words from the adults?
49:55To find out, they must compare them with pup calls from earlier in the year to see if they've changed.
50:01So let's just play the call that we got from the pups for the badger two months ago versus the
50:08calls that we got from them today.
50:10Let's see if we can hear it.
50:21Yeah, again, very non-structured calls early in the season and highly structured calls later in the season.
50:28Looking at this spectrogram, you really see the difference.
50:31You really do.
50:32Very detailed in the adult call.
50:33Yeah, very detailed.
50:34And again, look at how the structure goes up and then there's kind of a little drop and a little
50:40platform
50:40and then it drops down again compared to just going up and down in frequencies here.
50:46What we saw at the beginning of the season was that the pups gave very nonspecific, generic calls.
50:52And now these same pups are giving highly structured calls.
50:56So clearly the pups have learned in just two months how to adapt their calls so that they sound the
51:03same as the adult calls.
51:04Let's do the same thing with the coyote.
51:06Yeah, let's do that for the coyote.
51:08That should be interesting.
51:10Here we go.
51:12Wow.
51:15Again, nonspecific just squeaks versus a lot of acoustic structure.
51:20That's really very impressive.
51:22The calls are longer in duration as well.
51:23Yeah, the calls are longer in duration.
51:25Probably because they contain a lot more information in them.
51:31I think this shows that learning is actually going on because clearly we went from very generic nonspecific calls
51:40to very specific calls in just a short period of time.
51:44And I don't think that there's another explanation other than learning.
51:49It is possible that there's a genetic program that causes the maturation of the vocal tract.
51:55But I think that's relatively unlikely compared to the possibility of learning.
51:59They look differently at prairie dogs and not see them as just vermin.
52:04Prairie dogs have a very complicated social system.
52:07They have to have some sense of the relationships between each other in order to maintain this social system.
52:15They also have this complex language and they have to have some kind of intellectual structure in order to be
52:22able to understand this language as well.
52:24So the two things combined says to us that prairie dogs are really very complex animals.
52:31After 30 years of research, Conn has all the information he needs to help prove his bold claim that prairie
52:38dogs have the most sophisticated language in the animal world.
52:45At last, the prairie dogs can step from the shadow of the bison and take center stage as the true
52:52hero of the prairies.
52:54And they have one man to thank for that.
53:17And Natural World is back on Wednesday next week at the same time.
53:21Still to come tonight, stay with us as Horizon is rolling back the years.
53:25It's next.